In vitro performance of prefilled CO absorbers with the Zeus®.

Low fresh gas flows (FGFs) decrease the use of anesthetic gases, but increase CO absorbent usage. CO absorbent usage remains poorly quantified. The goal of this study is to determine canister life of 8 commercially available CO absorbent prepacks with the Zeus. Pre-packed CO canisters of 8 different brands were tested in vitro: Amsorb Plus, Spherasorb, LoFloSorb, LithoLyme, SpiraLith, SpheraSorb, Drägersorb 800+, Drägersorb Free, and CO2ntrol. CO (160 mL min) flowed into the tip of a 2 L breathing bag that was ventilated with a tidal volume of 500 mL, a respiratory rate of 10/min, and an I:E ratio of 1:1 using the controlled mechanical ventilation mode of the Zeus (Dräger, Lubeck, Germany). In part I, canister life of 5 canisters each of 2 different lots of each brand was determined with a 350 mL min FGF. Canister life is the time it takes for the inspired CO concentration (FCO) to rise to 0.5%. In part II, canister life was measured accross a FGF range of 0.25 to 4 L min for Drägersorb 800+ (2 lots) and SpiraLith (1 lot). In part III, the calculated canister life per 100 g fresh granule content of the different brands was compared between the Zeus and (previously published data for) the Aisys. In vitro canister life of prefilled CO absorber canisters differed between brands, and depended on the amount of CO absorbent and chemical composition. Canister life expressed as FCU (the fraction of the canister used per hour) was proportional to FGF over 0.2-2 L min range only, but was non-linear with higher FGF: FCU was larger than expected with FGF > 2 L min, and even with FGF > minute ventilation FCU did not become zero, indicating some CO was being absorbed. Canister life on a per weight basis of the same brand is higher with the Zeus than the Aisys. Canister life of prefilled CO absorber canisters differs between brands. The FCU-FGF relationship is not linear across the entire FGF range. Canister life of prepacks of the same brand for the Zeus and Aisys differs, the exact etiology of which is probably multifactorial, and may include differences in the absolute amount of absorbent and different rebreathing characteristics of the machines.